Intramuscular myxoma of the deltoid muscle: report of a case

Abstract

Intramuscular myxoma is a rare, benign lesion of mesenchymal origin, affecting the skeletal muscles. We report the case of a 75-year-old woman presenting with a mass of the right deltoid region. On the MRI examination it was interpreted as a lipomatous lesion. She underwent marginal excision. The pathological examination revealed the diagnosis of intramuscular myxoma.

BACKGROUND

The term myxoma was first used by Virchow in 1863 to describe a lesion resembling the mucinous substance of the umbilical cord.¹ Diagnostic criteria were established in 1948 by Stout, who defined myxoma as a true neoplasm composed of a paucity of stellate cells in a loose myxoid stroma of reticulin and collagen fibres, with poor vascularity.^2–4 A mucoid material of mucopolysaccharides separates the cells and fibres from one another.^2,3 The most frequent site of occurrence of myxoma is within the myocardium. In 1965 the first myxomas located in muscle were described.⁵ Most extracardiac soft-tissue myxomas occur in the musculature of the extremities.⁶ In this report, we describe the case of a 75-year-old woman presenting with a mass in the right deltoid region. On the MRI examination it was misinterpreted as a lipomatous lesion, but after sugery the pathological examination revealed an intramuscular myxoma.

CASE PRESENTATION

A 75-year-old woman presented with a slowly growing mass of the right deltoid region, of long standing (6 years). She described a trauma of the arm 2 years before the onset of the mass. She had a medical history of hypertension, hyperlipidaemia and duodenal ulcer. On physical examination the lesion was found to be 7×4 cm in size, firm, mobile and painless. MRI showed a well-circumscribed mass located in the deltoid muscle, suggesting a lipomatous nature (fig 1A,B). On surgical operation, the tumour appeared to be an encapsulated gelatinous mass, encased within the muscle (fig 1C). It was easily separated from the muscle fibres and was locally excised. The postoperative course was normal.

Figure 1.

A) MRI showing a homogeneous, well-circumscribed mass in the right deltoid muscle (coronal sections). B) Axial MRI sections. C) The lesion after local excision. D) Microscopic examination. The tumour is composed of abundant extracellular myxoid material (H&E ×4). E) Microscopic examination. Characteristic features are the paucity of stromal cells and vascular structure (H&E ×20). F) At the periphery of the tumour are residual bundles of skeletal muscle (H&E ×10). G) Immunohistochemistry (×40). CD34 positivity.

Microscopic examination showed a paucicellular lesion, with scarce spindle or stellate cells enmeshed within an abundant extracellular myxoid stroma (alcian-positive, hyaluronidase-sensitive). No cellular atypia or mitotic activity was evident. The reticulin fibre network was delicate. The vasculature was sparse and consisted of thin-walled capillary vessels (fig 1D,E). The lesion was partially delimited by bundles of skeletal muscle (fig 1F). On immunohistochemistry, the lesion was S100 negative and CD34 positive (fig 1G).

Ten months after surgery, there is no evidence of recurrence.

DISCUSSION

Soft-tissue myxomas have been classified as intramuscular myxoma, juxta-articular myxoma, superficial angiomyxoma, aggressive angiomyxoma and nerve sheath myxoma.⁷ Intramuscular myxomas are rare, benign soft-tissue tumours affecting patients 40–70 years old (60% of cases are in women).^7,8 They have an incidence of around 0.1–0.13 cases per 100 000 people.^4,7 They are found in skeletal muscles. In descending order of occurrence, the lesion is most frequently located in the large muscles of the thigh, shoulder, buttocks or upper arm.⁹ However, there are also reports of intramuscular myxomas in the hand, face, head, neck, tongue, and abdominal and paraspinal muscles.⁷ The tumour is completely surrounded by skeletal muscle or is attached to the overlying fascia.¹⁰ Clinically, the tumour presents as a firm, painless, palpable, slowly enlarging mass, slightly mobile and sometimes fluctuant.⁹ The aetiology is unknown, but a previous history of trauma is often reported.¹⁰ Intramuscular myxomas have also been described in association with monostotic and polyostotic fibrous dysplasia in Mazabraud syndrome^11,12 and McCune–Albright syndrome.⁷ Clinical diagnosis is difficult before biopsy or tumour excision. Plain radiographs are usually normal.¹⁰ Ultrasound and CT scanning have been used in the past in the differential diagnosis of the lesion. More recently MRI has supplanted these because of its superior detection and evaluation of soft-tissue masses.⁴ MRI characteristics of intramuscular myxomas include low T1-weighted and increased T2-weighted signal, intratumoral cysts, perilesional fat ring and surrounding muscular oedema. A homogeneous and moderate enhancement of the signal after injection with gadolinium is observed.^13–16 Lesions with abundant fluid or myxoid tissue may have a similar MRI appearance.¹⁷

Local excision with tumour-free margins provides an excellent result with a low incidence of local recurrence.¹⁸ Although imaging techniques are helpful, the correct diagnosis can be made only on histological examination. Histologically, the differential diagnosis includes a reactive lesion, such as myxoid nodular fasciitis, and also some mucoid sarcomas (myxoid malignant fibrous histiocytoma or myxoid liposarcoma).^4,8,15,16 In this context, we emphasise the role of the radiologist and the pathologist in a careful differential diagnosis, in order to avoid destructive surgery and inappropriate treatments.

LEARNING POINTS

• Intramuscular myxoma is rare, benign lesion of mesenchymal origin, most frequently located in the large muscles of the thigh, shoulder, buttocks or upper arm.

• The tumour presents as a firm, painless, palpable, slowly enlarging mass, slightly mobile and sometimes fluctuant.

• The aetiology is unknown, but a previous history of trauma is often reported.

• Clinical diagnosis is difficult before biopsy or tumour excision. Ultrasound and CT scan have been used in the differential diagnosis of the lesion. More recently MRI has supplanted them because of its superior detection and evaluation of soft-tissue masses.

• Local excision with tumour-free margins provides an excellent result with low incidence of local recurrence.

• Although imaging techniques are helpful, the correct diagnosis can be made only on histological examination. Histologically, the differential diagnosis includes a reactive lesion, such as myxoid nodular fasciitis, but also some mucoid sarcomas

• We emphasise the role of radiologist and pathologist in a careful differential diagnosis, in order to avoid destructive surgery and inappropriate treatments.